If I am asked what we are fighting for, I can reply in two sentences. In the first place, to fulfil a solemn international obligation … an obligation of honor which no self-respecting man could possibly have repudiated. I say, secondly, we are fighting to vindicate the principle that small nationalities are not to be crushed in defiance of international good faith at the arbitrary will of a strong and overmastering Power.

Premier Asquith, Statement, to House of Commons, Declaration of War with Germany, August 4, 1914.

Nothing will bring American sympathy along with us so much as American blood shed in the field.

The Great War differed from all ancient wars in the immense power of the combatants and their fearful agencies of destruction, and from all modern wars in the utter ruthlessness with which it was fought. … Europe and large parts of Asia and Africa became one vast battlefield on which after years of struggle not armies but nations broke and ran. When all was over, Torture and Cannibalism were the only two expedients that the civilized, scientific, Christian States had been able to deny themselves: and they were of doubtful utility.

Winston Churchill, From The World Crisis, 1911-1918 : Chapter I (The Vials of Wrath), Churchill, Butterworth (1923).

After the end of the World War of 1914 there was a deep conviction and almost universal hope that peace would reign in the world. The heart's desire of all the peoples could have easily been gained by steadfastness in righteous convictions, and by reasonable common sense and prudence. The phrase "the war to end war" was on every lip, and measures had been taken to turn it into reality. President Wilson, wielding, as was thought, the authority of the United States, had made the conception of a League of Nations dominant in all minds. The British Delegation at Versailles moulded and shaped his idea into an Instrument which will for ever constitute a milestone in the hard march of man. The victorious Allies were at that time all-powerful, so far as their outside enemies were concerned. They had to face grave internal difficulties and many riddles to which they did not know the answer, but the Teutonic Powers in the great mass of Central Europe were prostrate before them, and Russia, already shattered by the German flail, was convulsed by civil war and falling into the grip of the Bolshevik or Communist Party.

Winston Churchill, From The Second World War: Volume 1: The Gathering Storm, Churchill, Houghton Mifflin (1948)

If you hadn't entered the World War we would have made peace with Germany early in 1917. Had we made peace then there would have been no collapse in Russia followed by communism, no break-down in Italy followed by fascism, and Germany would not have signed the Versailles Treaty, which has enthroned nazi-ism in Germany. In other words, if America had stayed out of the war all of these "isms" wouldn't today be sweeping the Continent of Europe and breaking down parliamentary government, and if England had made peace early in 1917, it would have saved over 1,000,000 British, French, American, and other lives.

Attributed to Winston Churchill, but denied by him. William Griffin, sworn statement (September 8, 1939), reprinted in the Congressional Record (October 21, 1939), vol. 84, p. 686. Griffin, publisher of the New York Enquirer, said the conversation had taken place in London during August 1936. Griffin brought a $1,000,000 libel suit against Churchill in October 1939, but the charges were dismissed on October 21, 1942, when Griffin or his lawyers failed to appear when the case was called. At that time Griffin was under indictment in Washington, D.C., on charges of conspiring to lower the morale of the armed forces of this country. In his answer to the suit, Churchill admitted the 1936 interview, but denied the statement. The New York Times (October 22, 1942), p. 13. The proceedings against Griffin were later quashed after a hearing in federal court on January 26, 1944.

The Nation has need of all that can be contributed to it through the best efforts of all its citizens. The colored people have repeatedly proved their devotion to the high ideals of our country. They gave their services in the war with the same patriotism and readiness that other citizens did. The records of the selective draft show that somewhat more than 2,250,000 colored men were registered. The records further prove that, far from seeking to avoid participation in the national defense, they showed that they wished to enlist before the selective service act was put into operation, and they did not attempt to evade that act afterwards.

Are we virtuous merely because we are restrained by the fetters of the law? We hear men prophecy that this war means the death of Christianity and an era of Pandeism or perhaps even the destruction of all which we call modern civilization and culture. We hear men predict that the ultimate result of the war will be a blessing to humanity.

The transformation came on even more abruptly than is usually realized. World War I and the postwar revolutions still formed part of the nineteenth century. The conflict of 1914-18 merely precipitated and immeasurably aggravated a crisis that it had not created. But the roots of the dilemma could not be discerned at the time; and the horrors and devastations of the Great War seemed to the survivors the obvious source of the obstacles to international organization that had so unexpectedly emerged.

Some of us still recall World War I, which awakened our generation to the fact that history was not a matter of the past, as a thoughtless philosophy of the hundred years’ peace would have us believe. And once started, it did not cease to happen. I will seek to evoke the scenes we have witnessed and take the measure of our frustrations. Great triumphs and grave disappointments have been met with. However, it is not a balance of our experiences, achievements and omissions that stands to question; nor am I scanning the horizon for a mere break. The time has come to take note of a much bigger change.

The First World War killed fewer victims than the Second World War, destroyed fewer buildings, and uprooted millions instead of tens of millions — but in many ways it left even deeper scars both on the mind and on the map of Europe. The old world never recovered from the shock.

Edmond Taylor, in The Fossil Monarchies.

It is a fearful thing to lead this great peaceful people into war, into the most terrible and disastrous of all wars, civilization itself seeming to be in the balance. But the right is more precious than peace, and we shall fight for the things which we have always carried nearest our hearts, for democracy, for the right of those who submit to authority to have a voice in their own governments, for the rights and liberties of small nations, for a universal dominion of right by such a concert of free peoples as shall bring peace and safety to all nations and make the world itself at last free. To such a task we can dedicate our lives and our fortunes, everything that we are and everything that we have, with the pride of those who know that the day has come when America is privileged to spend her blood and her might for the principles that gave her birth and happiness and the peace which she has treasured. God helping her, she can do no other.

Woodrow Wilson, address to a joint session of Congress recommending that Germany's course be declared war against the United States (April 2, 1917), Albert Shaw, ed., The Messages and Papers of Woodrow Wilson (1924), vol. 1, p. 382–83.

God would never be cruel enough to create a cyclone as terrible as that Argonne battle. Only man would ever think of doing an awful thing like that. It looked like "the abomination of desolation" must look like. And all through the long night those big guns flashed and growled just like the lightning and the thunder when it storms in the mountains at home.
And, oh my, we had to pass the wounded. And some of them were on stretchers going back to the dressing stations, and some of them were lying around, moaning and twitching. And the dead were all along the road. And it was wet and cold. And it all made me think of the Bible and the story of the Anti-Christ and Armageddon.
And I'm telling you the little log cabin in Wolf Valley in old Tennessee seemed a long long way off.

Alvin C. York, in his account of 7 October 1918, in the Diary of Alvin York.

It have been one of the richest experiences of my life...feeling that I was being really useful to the boys on the other side.

Unidentified actress about working in a war factory. From an excerpt in Adriane Ruggiero, American Voices from World War I (2003), p. 79–80, citing Norma B. Kastl, "Wartime, the Place and the Girl", Independent magazine (unidentified issue).